Today, a variety of different hosts including plants, algae, fungi, stramenopiles and yeast are being investigated as means for commercial PUFA production. Genetic engineering has demonstrated that the natural abilities of some hosts (even those natively limited to linoleic acid (LA; 18:2 ω-6) or α-linolenic acid (ALA; 18:3 ω-3) fatty acid production) can be substantially altered to result in high-level production of various long-chain ω-3/ω-6 PUFAs. Accordingly, production of arachidonic acid (ARA; 20:4 ω-6), eicosapentaenoic acid (EPA; 20:5 ω-3) and docosahexaenoic acid (DHA; 22:6 ω-3) may require expression of a Δ8 desaturase.
The Δ8 desaturase enzymes identified thus far have the ability to convert both eicosadienoic acid (EDA; 20:2 ω-6) to dihomo-γ-linolenic acid (DGLA; 20:3 ω-6) and eicosatrienoic acid (ETrA; 20:3 ω-3) to eicosatetraenoic acid (ETA; 20:4 ω-3) (wherein ARA are EPA are subsequently synthesized from DGLA and ETA, respectively, following reaction with a Δ5 desaturase, while DHA synthesis requires subsequent expression of an additional C20/22 elongase and a Δ4 desaturase).
Based on the role Δ8 desaturase enzymes play in the synthesis of e.g., ARA, EPA and DHA, considerable effort has been made to identify and characterize these enzymes from various sources. Initial efforts have focused on the isolation and characterization of Δ8 desaturases from Euglena gracilis; and, several sequence variations within the Euglena gracilis Δ8 desaturase have been reported (see, e.g., Wallis et al., Arch. Biochem. and Biophys., 365(2):307-316 (1999); PCT Publication No. WO 2000/34439; U.S. Pat. No. 6,825,017; PCT Publication No. WO 2004/057001). Additionally, commonly owned, co-pending U.S. application Ser. No. 11/166,003 and U.S. Pat. No. 7,256,033 disclose amino acid and nucleic acid sequences for a Euglena gracilis Δ8 desaturase. In other work commonly owned, co-pending applications U.S. patent application Ser. No. 11/635,258 and Ser. No. 11/951,697 describe a synthetically engineered mutant Δ8 desaturase, derived from Euglena gracilis. 
U.S. Publication No. 2005/0273885 discloses amino acid and nucleic acid sequences for a Δ8 desaturase enzyme from Pavlova salina and commonly owned and co-pending application U.S. patent application Ser. No. 11/737,772 discloses amino acid and nucleic acid sequences for a Δ8 desaturase enzyme from Pavlova lutheri (CCMP459), whereas U.S. patent application Ser. No. 11/876,115 discloses amino acid and nucleic acid sequences for Δ8 desaturase enzymes from Tetruetreptia pomquetensis CCMP1491, Eutreptiella sp. CCMP389 and Eutreptiella cf—gymnastica CCMP1594. Sayanova et al. (FEBS Lett., 580:1946-1952 (2006)) describe the isolation and characterization of a cDNA from the free living soil amoeba Acanthamoeba castellanii that, when expressed in Arabidopsis, encodes a polypeptide having C20 Δ8 desaturase activity.
Despite the disclosures cited above, there is a need for additional genes encoding polypeptides having Δ8 desaturase activity as it is only through genetic variation that a wide variety of host cells may be optimized for PUFA production. Applicants address the stated need herein by reporting the isolation of genes encoding Δ8 fatty acid desaturases from Euglena anabaena. 